ListGrid.willFetchData(null) fails

[d.cavestro]

Hi,
I have to test if a listGrid will fetch data, and sometimes, I have no filtering criteria to apply, so I pass null to willFetchData, but it complains

00:14:53.064 [ERROR] Uncaught exception escaped
com.google.gwt.core.client.JavaScriptException: (String): Invoking an instance method on a null instance
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at com.google.gwt.dev.shell.ModuleSpace.createJavaScriptException(ModuleSpace.java:65)
at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:60)
at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:157)
at com.google.gwt.dev.shell.BrowserChannel.reactToMessagesWhileWaitingForReturn(BrowserChannel.java:1714)
at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:165)
at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:120)
at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:507)
at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:264)
at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91)
at com.smartgwt.client.widgets.grid.ListGrid.willFetchData(ListGrid.java)
at com.mycompany.project.client.Test$1.execute(Test.java:50)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:157)
at com.google.gwt.dev.shell.BrowserChannel.reactToMessagesWhileWaitingForReturn(BrowserChannel.java:1714)
at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:165)
at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:120)
at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:507)
at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:264)
at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91)
at com.google.gwt.core.client.impl.Impl.apply(Impl.java)
at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:188)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:157)
at com.google.gwt.dev.shell.BrowserChannel.reactToMessages(BrowserChannel.java:1669)
at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:401)
at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:222)
at java.lang.Thread.run(Thread.java:619)

This is a simple test snippet

listGrid.fetchData (null, new DSCallback() {
	
    @Override
    public void execute (DSResponse response, Object rawData, DSRequest request) {
        GWT.log ("async callback called for fetchData (a server fetch has just been done)");
        GWT.log ("now we can proceed testing willFetchData");
        //never get this log, cause willFetchData fails
        GWT.log ("willFetchData returned: " + listGrid.willFetchData (null));
        
    }
});

Is this a known behavior? If so, why I can pass null to fetchData (to pass a callback but not a criteria) and not to willFetchData? And how can I execute some - say, cleanup - code after both an async fetch (real fetch) and a sync one (no fetch, cache hit)?
I proposed a solution in http://forums.smartclient.com/showpo...18&postcount=4 but even that solution could be undermined by this issue (I could add a try/catch, but now I suspect to misuse willFetchData)

I've attached a complete test case.

At client side I'm using
SmartClient Version: 8.0/LGPL Development Only (built 2010-10-18)
(reproduced even on SC_SNAPSHOT-2010-10-11/LGPL Development Only (built 2010-10-11))
GWT 2.0.4
Firefox 3.6.9

at server side Grails 1.3.4

Kind regards
Davide

EDIT:
I found a workaround to the exception (passing an empty Criteria obtained calling the default constructor).
This is a snippet of the test modified to prevent the exception

final Criteria emptyCriteria = new Criteria ();
GWT.log ("willFetchData returned: " + listGrid.willFetchData (emptyCriteria));
listGrid.fetchData (emptyCriteria, new DSCallback() {
    
    @Override
    public void execute (DSResponse response, Object rawData, DSRequest request) {
        GWT.log ("async callback called for fetchData (a server fetch has just been done)");
        GWT.log ("now we can proceed testing willFetchData");
        
        final Boolean willFetchData = listGrid.willFetchData (emptyCriteria);
        GWT.log ("the second willFetchData returned: " + willFetchData);
        
        listGrid.fetchData (emptyCriteria, new DSCallback() {
            
            @Override
            public void execute (DSResponse response, Object rawData, DSRequest request) {
                if (!willFetchData) {
                    throw new RuntimeException ("Unexpected server fetch");
                }
                GWT.log ("very strange... another server fetch has just been done");
            }
        });
    }
});

and the resulting behavior seems correct (tested only for SmartClient Version: SC_SNAPSHOT-2010-10-11/LGPL Development Only (built 2010-10-11))
So I think the problem still applies even though with a different phrasing: is it legal to pass a null Criteria reference? If so: when?

[d.cavestro]

Isormorphic?

[Isomorphic_Paul]

Looks like you already got this working.

However for completeness, the answer is - you can always pass an explicit empty criteria object in to any methods that take a criteria parameter.

null is typically treated the same as empty criteria by methods that have a criteria parameter and we'll look into why this isn't working in the case you describe offline but the correct way to do this is to use an empty Criteria object.

[Isomorphic]

Support for null values for Criteria type parameters has been added.